The present invention relates to the field of catalytic particles, and more particularly to colloidal metal particles used as catalysts.
In the art of forming catalytic colloidal metal particles, U.S. Pat. No. 4,425,261 of Stenius et al. discloses a method for preparing particles of metal in the platinum group whereby a metal salt is dissolved in a microemulsion, and the salt is reduced by hydrazine to form elemental metal particles. Several problems are associated with metal particles prepared in accordance with the Stenius et al. method. One problem is that production of iridium catalysts is very difficult. Another problem is that the platinum group particles that are formed are not stable in solution. Another problem is that the suspended metal particles will aggregate when the suspending solution is diluted.
In "Radiation Induced Preparation of Metal Catalysts: Iridium Aggregates", by Belloni in Nouveau Journal De Chimie, Vol. 6, No. 11-1982, p. 507, there is a disclosure that elemental iridium particles are prepared by exposing an aqueous solution of hexachloroiridic acid, in the presence of polyvinyl alcohol surfactant, to a radioactive cobalt-60 source. The dangers and environmental problems associated with radioactive sources are well known and best avoided.
Other patents disclose methods of preparing catalytic particles which are not elemental metal particles. These patents include U.S. Pat. Nos. 4,390,514 and 4,339,345.
Catalytic metal particles are employed in a number of ways in the prior art. For example, the catalytic particles are often supported on catalyst substrates that are contacted with the reactants whose reaction the particles are to catalyze. Other prior art methods either bring catalytic particles to the reactants or bring the reactants to the catalytic particles. It would be desirable, however, if the catalytic particles could be made in situ in the presence of the reactants.
The efficient use of expensive material implies that small, stable colloidal particles be formed in media appropriate to the desired chemical reaction. Thus, forming colloidal particles that are stable in water is not useful if the desired chemical reaction is to take place in toluene. It would be desirable, therefore, if colloidal particles could be formed that are stable in both aqueous and nonaqueous solvents.